Washington — President Obama’s appeal among independent voters appears to be slipping, and as a result, he has lost his double-digit lead in polls that measure whether the president or an unnamed Republican is favored to win the White House in 2012.

A new Pew Research Center poll among registered voters, conducted July 20-24, found that 41 percent favor Mr. Obama in next year's presidential election, while 40 percent favor a Republican candidate. In May, Obama held an 11-point lead over a generic Republican candidate.

“This shift is driven by a steep drop-off in support for Obama among independent voters,” Pew Research president Andrew Kohut said in a statement. In the July Pew poll, 31 percent of independent voters favor Obama’s reelection, down from 42 percent in May and 40 percent in March.

The numbers, while unwelcome news for the White House, probably do not come as a surprise. The Real Clear Politics average of major polls currently has the generic Republican candidate favored over Obama, 44.7 percent to 41 percent. One notable exception is the NBC News/Wall Street Journal poll, which has the president three points ahead – 42 to 39 percent – in a test race against an unnamed Republican.

The state of the economy, along with its effect on public opinion, is a key reason for the president’s lackluster poll numbers, Pew said. “By most measures Barack Obama faces a more somber public mood and a more troubled economy than did any” recent president, the research organization said. Just 8 percent of those surveyed say the national economy is in excellent or good shape, and 38 percent rate their personal finances positively, Pew notes.

The ultimate shape of the 2012 race for the White House will depend on who is nominated by the Republican Party. On that question “there is no greater clarity,” Mr. Kohut said. Only about a quarter of voters have thought seriously about the 2012 election, Pew found. Among Republicans and Republican-leaning independents, former Massachusetts Gov. Mitt Romney leads with 21 percent, followed by Texas Gov. Rick Perry at 12 percent, former Alaska Gov. Sarah Palin at 11 percent, and Minnesota Rep. Michele Bachmann, also at 11 percent. Governor Perry and Ms. Palin have not announced presidential candidacies.

While Representative Bachmann is not the Republican front-runner, she is the most visible candidate in the GOP field, the Pew survey found. When asked which candidate they had heard about most, 23 percent of Americans gave Bachmann's name. Mr. Romney, at 16 percent, was the next most frequently mentioned.

The poll's overall margin of error was plus or minus 3.5 percentage points.